Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 252203 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 603 PM EDT MON AUG 25 2014 .SYNOPSIS... HIGH PRESSURE WILL CENTER OVER THE REGION TONIGHT AND PERSIST THROUGH WEDNESDAY BEFORE A WEAK COLD FRONT PASSES THROUGH THE AREA WEDNESDAY NIGHT. HIGH PRESSURE WILL CROSS THE NORTHERN MID-ATLANTIC THURSDAY AND LINGER OFFSHORE INTO THE WEEKEND. && .NEAR TERM /THROUGH TUESDAY/... AS OF 18Z...1022MB SFC HIGH CENTER EXTENDS FROM NRN NJ TO DC. A LIGHT ONSHORE FLOW PERSISTS OVER THE AREA...PARTICULARLY SRN PORTIONS OF THE CWA. UPR HIGH IS OVER MO. TEMPS AROUND 80F WITH FAIR CU...BY MANY ACCOUNTS A PLEASANT LATE AUGUST DAY. TONIGHT...MORE VALLEY FOG OVERNIGHT AS TEMPERATURES DROP INTO THE UPR 40S TO LOW 50S WEST OF THE BLUE RIDGE. EAST OF THE BLUE RIDGE... DECOUPLED CONDITIONS WILL ALLOW TEMPERATURES TO DROP INTO THE MID TO UPR 50S...MID TO UPR 60S NEARSHORE AND URBAN AREAS. TUESDAY...WARMER MID-LEVEL AIR OVER THE MIDWEST WILL PUSH EAST OVERNIGHT... MAKING FOR A WARMER...YET STILL SUNNY. AN INCREASE OF AFTERNOON 850MB TEMPS FROM 14C TO 16C SHOULD RESULT IN MID TO UPR 80S MAX TEMPS. FEW FAIR CU AGAIN. && .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/... WEDNESDAY...WEAK COLD FRONT APPROACHES FROM THE NORTHWEST THROUGH THE DAY. BETTER MIXING AND 18C 850MB TEMPS SHOULD ALLOW MAX TEMPS AROUND 90F. ISO/SCT THUNDERSTORMS ARE EXPECTED THAT EVENING WITH THE ACTIVITY AS INSTABILITY INCREASES WITH LI OF -3 TO -5. && .LONG TERM /THURSDAY THROUGH MONDAY/... A STALLED FRONTAL BOUNDARY SOUTH AND EAST OF THE AREA WILL BRING A CHANCE OF SHOWERS TO THE SOUTHERN PORTIONS OF THE POTOMAC HIGHLANDS AND SHENANDOAH VALLEY THURSDAY AFTERNOON AND EVENING. HIGH PRESSURE WILL BUILD INTO THE MID ATLANTIC FROM THE NORTH THURSDAY NIGHT AND REMAIN THROUGH FRIDAY...FORCING THE SURFACE BOUNDARY FURTHER SOUTH AND KEEPING THE ENTIRE CWA DRY. AS THIS HIGH PRESSURE MOVES EAST THE SURFACE BOUNDARY WILL RETURN NORTH...BRINGING A CHANCE OF RAIN TO THE AREA DURING THE DAY SATURDAY. WARM AND HUMID AIR WILL FILL IN AS THIS FRONT MOVES THROUGH THE AREA DURING THE DAY...LEADING TO INCREASED INSTABILITY AND A CHANCE OF THUNDERSTORMS SATURDAY EVENING. A SHORTWAVE TROUGH WILL LIFT A SURFACE LOW THROUGH THE GREAT LAKES REGION AND ACROSS THE NORTHEAST SUNDAY. THE ASSOCIATED COLD FRONT WILL APPROACH...AND STALL OVER OR NEAR THE AREA BY SUNDAY AFTERNOON...BRINGING THE CHANCE FOR SHOWERS AND THUNDERSTORMS TO THE MID-ATLANTIC SUNDAY AFTERNOON THROUGH MONDAY. TEMPS WILL BE NEAR TO SLIGHTLY BELOW NORMAL FRIDAY AND SATURDAY...WITH HIGHS IN THE LOWER TO MID 80S AS WE STAY ON THE COOL SIDE OF THE SURFACE BOUNDARY. HIGHS WILL INCREASE TO A COUPLE OF DEGREES ABOVE NORMAL...IN THE UPPER 80S...AS THE BOUNDARY MOVES TO OUR NORTH AND PREFRONTAL SOUTHERLY FLOW TAKES OVER SATURDAY AND SUNDAY. LOWER 80S SHOULD RETURN FOR THE BEGINNING OF THE WORKWEEK AFTER THE COLD FRONT MOVES THROUGH. && .AVIATION /22Z MONDAY THROUGH SATURDAY/... HIGH PRESSURE/VFR INTO WEDNESDAY OUTSIDE OF MORNING FOG (PARTICULARLY FOR KMRB AND KCHO). WEAK COLD FRONT CROSSES WEDNESDAY NIGHT WITH SCT TSRA. CONFIDENCE IS LOW IN THE OCCURRENCE OF ANY HAZARDS TO AVIATION IN THE LONG TERM. && .MARINE... ONSHORE FLOW CONTINUES THROUGH TOMORROW AS HIGH PRESSURE PERSISTS TO THE NORTH. LIGHT AND VARIABLE FLOW UNDER THE HIGH LATE TUESDAY INTO WEDNESDAY. WEAK COLD FRONT CROSSES THE WATERS WEDNESDAY NIGHT BRINGING SCATTERED THUNDERSTORMS. CONFIDENCE IS LOW IN THE OCCURRENCE OF ANY MARINE HAZARDS THROUGH THE LONG TERM. && .TIDES/COASTAL FLOODING... WATER LEVEL DEPARTURES HOVERING AROUND 1 FT ABOVE NORMAL. TIDES THIS CYCLE HAVE BEEN COMING IN UNDER THE THRESHOLD FOR MINOR FLOODING. DC REMAINS THE ONE EXCEPTION. WE/VE PASSED LOW TIDE... AND THUS FAR THE HEC-RAS GUIDANCE SEEMS TO BE ON TRACK. EXPECT DIFFERENCES BY HIGH TIDE TO BE NO MORE THAN A FEW INCHES OFF... WHICH STILL WILL PLACE HIGH TIDE AT THE CRITICAL POINT FOR THE SW WATERFRONT. THEREFORE...HAVE OPTED TO ISSUE A COASTAL FLOOD ADVISORY FOR DC. SINCE SURROUNDING JURISDICTIONS NEED A HIGHER FORECAST...HAVE LEFT THEM OUT. PREFERRED HIGH TIDE IS TUESDAY MORNING. BASED ON CURRENT PROJECTIONS...SENSITIVE SITES ARE LIKELY TO HAVE MINOR COASTAL FLOODING AT THAT TIME. MAY BE MAKING THOSE HEADLINE DECISIONS BEFORE THE NIGHT IS DONE. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...COASTAL FLOOD ADVISORY UNTIL 11 PM EDT THIS EVENING FOR DCZ001. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...BAJ NEAR TERM...BAJ SHORT TERM...BAJ LONG TERM...CEB AVIATION...BAJ/CEB MARINE...BAJ/CEB TIDES/COASTAL FLOODING...HTS

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